title: Skepinone-L, a novel potent and highly selective inhibitor of p38 MAP kinase, effectively impairs platelet activation and thrombus formation.
abstract: OBJECTIVE
  Platelets are critically important for primary haemostasis and the major players in thrombotic vascular occlusion. Platelets are activated by agonists, such as thrombin and collagen-related peptide as well as second-wave mediators including thromboxane A2 via different intracellular signaling pathways resulting in degranulation, aggregation and thrombus formation. Platelet activation is paralleled by phosphorylation and activation of p38 MAPK. The limited specificity of hitherto known p38 MAPK inhibitors precluded safe conclusions on the precise role of p38 MAPK in the regulation of platelet function. The present study examined the impact of Skepinone-L, a novel and highly selective inhibitor of p38 mitogen-activated protein kinase (p38 MAPK), on platelet activation and thrombus formation.
  
  
  METHODS
  Experiments were performed in freshly isolated human platelets. Protein phosphorylation was quantified by Western blotting, thromboxane B2 synthesis by enzyme immunoassay, ATP release by ChronoLume luciferin assay, cytosolic Ca(2+) concentration by Fura-2 fluorescence-measurements, platelet aggregation by a light transmissions measurement and in vitro thrombus formation by a flow chamber.
  
  
  RESULTS
  Skepinone-L (1 μM) virtually abrogated the phosphorylation of platelet p38 MAPK substrate Hsp27 following stimulation with CRP (1 μg/ml), thrombin (5 mU/ml) or thromboxane A2 analogue U-46619 (1 μM). Furthermore, Skepinone-L significantly blunted activation-dependent platelet secretion and aggregation following threshold concentrations of CRP, thrombin and thromboxane A2 analogue U-46619. Skepinone-L did not impair platelet Ca(2+) signaling but prevented agonist-induced thromboxane A2 synthesis through abrogation of p38 MAPK-dependent phosphorylation of platelet cytosolic phospholipase A2 (cPLA2). Skepinone-L further markedly blunted thrombus formation under low (500-s) and high (1700-s) arterial shear rates.
  
  
  CONCLUSIONS
  The present study discloses a powerful inhibiting effect of p38 MAPK-blocker Skepinone-L on platelet activation and thrombus formation.
authors.affiliation: Department of Physiology, University of Tübingen, Gmelinstrasse 5, Tübingen, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Borst
authors.forename: Britta
authors.initials: B
authors.lastname: Walker
authors.forename: Patrick
authors.initials: P
authors.lastname: Münzer
authors.forename: Antonella
authors.initials: A
authors.lastname: Russo
authors.forename: Evi
authors.initials: E
authors.lastname: Schmid
authors.forename: Caterina
authors.initials: C
authors.lastname: Faggio
authors.forename: Boris
authors.initials: B
authors.lastname: Bigalke
authors.forename: Stefan
authors.initials: S
authors.lastname: Laufer
authors.forename: Meinrad
authors.initials: M
authors.lastname: Gawaz
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000494:pharmacology; D003986:Dibenzocycloheptenes / Q000494:pharmacology*; D016257:Fura-2 / Q000737:chemistry; D055551:HSP27 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D010455:Peptides / Q000494:pharmacology; D054467:Phospholipases A2 / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D015539:Platelet Activation / Q000187:drug effects; D010974:Platelet Aggregation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D033081:Shear Strength / Q000187:drug effects; D013917:Thrombin / Q000494:pharmacology; D013927:Thrombosis / Q000378:metabolism / Q000473:pathology; D013929:Thromboxane B2 / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D003986:Dibenzocycloheptenes; D055551:HSP27 Heat-Shock Proteins; D010455:Peptides; D047428:Protein Kinase Inhibitors; C435908:collagen-related peptide; C572387:skepinone-L; D013929:Thromboxane B2; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D000255:Adenosine Triphosphate; D048051:p38 Mitogen-Activated Protein Kinases; D054467:Phospholipases A2; D013917:Thrombin; D002118:Calcium; D016257:Fura-2